[Docs] Update Shell inline comments

[jsuarezruiz]

Description of Change

Update Shell inline docs.

[jknaudt21]

I love that we're making progress on documenting Shell. However, since this class receives a lot of traffic and views, I would encourage you to review the DotNet style guide: https://github.com/dotnet/dotnet-api-docs/wiki/Summary

The things that quickly standout for me thus far have been:

• Inconsistent verb tense. Some entries are in infinitive tense, while others are in present tense "Define" vs "Defines", "Get" vs "Gets". I think that everything should be in present tense
• References to other classes, properties, or methods within the class should be linked with a <see cref='''/> tag
• Paremeters are referencing their own types, which is not recommended by the style guide: https://github.com/dotnet/dotnet-api-docs/wiki/Parameters
• Some summaries seem to be quite thorough. Although it is awesome you're adding this detail, this is not entirely recommended as to how the docs should be structured: https://github.com/dotnet/dotnet-api-docs/wiki/Summary
• Boolean parameters and properties should follow the standard wording: https://github.com/dotnet/dotnet-api-docs/wiki/Summary%3A-Property, https://github.com/dotnet/dotnet-api-docs/wiki/Parameters%3A-Methods-and-constructors
• Make sure to delete the XML files behind some of the old documents!
• You might've already done this, but check out the conceptual docs for Shell (and subpages) for free wins on items and properties that have already been documented by Dave and could just be ported to API docs easily: https://learn.microsoft.com/en-us/dotnet/maui/fundamentals/shell/?view=net-maui-8.0

Nonetheless, other than these generic observations, things look good!

[jknaudt21]

Adding @davidbritch as a reviewer to help craft these docs to the best shape.

[jknaudt21]

Existing docs look good to me. I guess we can move the deleting the xml file and shifting the docs into another PR to no longer block this one